Tendons transmit force from the muscles to the bone, enabling movement, while ligaments connect bone to bone, providing stabilization. Sports or age-related injuries to tendons or ligaments are extremely common, and although the injury can be slowly repaired, the new tissue lacks the original biomechanical integrity. Although many studies have focused on the structure, composition, and organization of tendon and ligament tissues after birth, very little is known about their development during embryogenesis. The goal of this project is to discover the pathways regulating tendon and ligament formation and differentiation in the embryo. To accomplish this, we will use the zebrafish, a powerful genetic vertebrate model system. For Aim 1 of my proposal, I will perform a histological, ultrastructural, and molecular analysis of zebrafish tendons in the fin and cranial regions. I will develop live imaging assays with transgenic zebrafish to visualize tendon formation and morphogenesis over real developmental time, a technique that is unfeasible in other vertebrates. For Aim 2, I will perform forward genetic and high-throughput chemical screens to discover and characterize new pathways regulating tendon development. These studies will directly address the major questions in the field of tendon developmental biology, and may ultimately, aid in the development of new therapies for tendon or ligament injury. Because of my graduate and post-doctoral research experiences, I am in an ideal position to carry out this project. For my Ph.D., I worked in Dr. Leonard Zon's laboratory on hematopoiesis in the zebrafish where I learned genetic and chemical screening, positional cloning, transgenics, morpholinos, and many other zebrafish research techniques. During my postdoc in Dr. Cliff Tabin's lab, I initially studied limb patterning to gain insight into how limb tissues are first arranged, and have more recently focused on how mammalian tendons subsequently form and organize in the embryonic limb. The rich research environment, equipment and facilities available in the Genetics Department at Harvard Medical School lab along with support from my mentor, Dr. Tabin, and advisors, Dr. Zon, Dr. Andrew Lassar, and Dr. Caroline Shamu will allow me to complete my goals for the mentored phase of this proposal. Furthermore, this award will develop the tools and cultivate the skills necessary for success in an academic faculty position. Ultimately, this project will not only allow me to pursue an independent research plan from that of my mentor, but it also will create a unique niche for me as an independent investigator in the field of tendon biology.